Ventricular fibrillation: Mechanisms of initiation and maintenance

Ventricular fibrillation (VF) is the major immediate cause of sudden cardia c death. Traditionally, VF has been defined as turbulent cardiac electrical activity, which implies a large amount of irregularity in the electrical w aves that underlie ventricular excitation. During VF, the heart rate is too high (> 550 excitations/minute) to allow adequate pumping of blood. In the electrocardiogram (ECG), ventricular complexes that are ever-changing in f requency, contour, and amplitude characterize VE This article reviews preva iling theories for the initiation and maintenance of VF, as well as its spa tio-temporal organization. Particular attention is given to recent experime nts and computer simulations suggesting that VF may be explained in terms o f highly periodic three-dimensional rotors that activate the ventricles at exceedingly high frequency. Such rotors may show at least two different beh aviors: (a) At one extreme, they may drift throughout the heart at high spe eds producing beat-to-beat changes in the activation sequence. (b) At the o ther extreme, rotors may be relatively stationary, activating the ventricle s at such high frequencies that the wave fronts emanating from them breakup at varying distances, resulting in complex spatio-temporal. patterns of fi brillatory conduction. In either case, the recorded ECG patterns are indist inguishable from VE The data discussed have paved the way for a better unde rstanding of the mechanisms of VF in the normal, as well as the diseased, h uman heart.